Air-conditioning apparatus

ABSTRACT

An air-conditioning apparatus includes a fan configured to deliver air toward the outdoor heat exchanger, a power unit configured to supply electric power to the fan, a fan input detector configured to detect a physical value related to the electric power supplied to the fan, and a controller configured to control the four-way valve to switch between a first operation in which the outdoor heat exchanger functions as an evaporator and a second operation in which the outdoor heat exchanger functions as a condenser. The first operation is switched to the second operation when the physical value detected by the fan input detector is equal to or larger than a reference value. The controller adjusts the reference value so that the reference value when refrigerant flowing through the outdoor heat exchanger has a high temperature is smaller than the reference value when the refrigerant has a low temperature.

TECHNICAL FIELD

The present invention relates to an air-conditioning apparatus.

BACKGROUND ART

A conventional air-conditioning apparatus detects, in a heatingoperation, the current value of an outdoor fan motor and the rotationspeed of an outdoor fan, and determines whether to start a defrostingoperation based on whether the current value of the outdoor fan motorbecomes equal to or larger than a reference current value or therotation speed of the outdoor fan decreases by a predetermined rotationspeed (refer to Patent Literature 1).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application PublicationNo. 2009-58222

SUMMARY OF INVENTION Technical Problem

In the air-conditioning apparatus disclosed in Patent Literature 1, thereference current value is determined in advance and cannot be changedwith taken into account decrease in a fan input due to decrease in thefan rotation speed when the efficiency of the outdoor fan motor degradesby aging. This configuration prevents transition to the defrostingoperation at appropriate timing in the heating operation. In otherwords, defrosting cannot be performed efficiently.

The present invention is intended to solve the above-described problemand provide an air-conditioning apparatus that performs a defrostingoperation more efficiently than conventionally practiced.

Solution to Problem

An air-conditioning apparatus according to an embodiment of the presentinvention includes, by connecting, a compressor, an outdoor heatexchanger, an indoor heat exchanger, and a switching device, theswitching device being provided closer to a discharge side of thecompressor than the outdoor heat exchanger and provided closer to thedischarge side of the compressor than the indoor heat exchanger. Theair-conditioning apparatus includes a fan configured to deliver airtoward the outdoor heat exchanger, a power unit configured to supplyelectric power to the fan, a fan input detector configured to detect aphysical value related to the electric power supplied to the fan, and acontroller configured to control the switching device to switch betweena first operation in which the outdoor heat exchanger functions as anevaporator and a second operation in which the outdoor heat exchangerfunctions as a condenser. The first operation is switched to the secondoperation when the physical value detected by the fan input detector isequal to or larger than a reference value. The controller adjusts thereference value so that the reference value when refrigerant flowingthrough the outdoor heat exchanger has a high temperature is smallerthan the reference value when the refrigerant has a low temperature.

Advantageous Effects of Invention

The air-conditioning apparatus according to an embodiment of the presentinvention includes the controller configured to control the switchingdevice to switch between the first operation in which the outdoor heatexchanger functions as an evaporator and the second operation in whichthe outdoor heat exchanger functions as a condenser. The first operationis switched to the second operation when the physical value detected bythe fan input detector is equal to or larger than the reference value.The controller adjusts the reference value so that the reference valuewhen the refrigerant flowing through the outdoor heat exchanger has ahigh temperature is smaller than the reference value when therefrigerant flowing through the outdoor heat exchanger has a lowtemperature. With this configuration, a defrosting operation can bestarted at an appropriate timing while a heating operation is beingperformed. Thus, the defrosting operation can be performed moreefficiently than has been conventionally practiced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating an air-conditioning apparatus100 according to Embodiment 1 of the present invention.

FIG. 2 is a diagram illustrating change in a frosting amount and totalelectric power with elapsed time in the air-conditioning apparatus 100according to Embodiment 1 of the present invention.

FIG. 3 is a diagram illustrating change in the frosting amount and totalcurrent value with elapsed time in the air-conditioning apparatus 100according to Embodiment 1 of the present invention.

FIG. 4 is a diagram illustrating change in an electric power amount withelapsed time in the air-conditioning apparatus 100 according toEmbodiment 1 of the present invention.

FIG. 5 is a diagram illustrating change in a total electric power amountwith elapsed time in the air-conditioning apparatus 100 according toEmbodiment 1 of the present invention.

FIG. 6 is a schematic view illustrating a state in which frost exists onan outdoor heat exchanger 3 of the air-conditioning apparatus 100according to Embodiment 1 of the present invention.

FIG. 7 is a diagram illustrating a relation between a relative humidityφ and a frost density ρ in the air-conditioning apparatus 100 accordingto Embodiment 1 of the present invention.

FIG. 8 is a diagram illustrating a relation between a refrigeranttemperature and a necessary defrosting heat amount in theair-conditioning apparatus 100 according to Embodiment 1 of the presentinvention.

FIG. 9 is a diagram illustrating change in the frequency of a compressor1 with elapsed time in the air-conditioning apparatus 100 according toEmbodiment 1 of the present invention.

FIG. 10 is a diagram illustrating change in the frequency of thecompressor 1 with elapsed time in the air-conditioning apparatus 100according to Embodiment 1 of the present invention.

DESCRIPTION OF EMBODIMENTS Embodiment 1

An air-conditioning apparatus 100 of the present invention will bedescribed in detail below with reference to the drawings. The sizes ofcomponents in the drawings are in a relation different from that oftheir actual sizes in some cases. In the drawings, any componentsdenoted by an identical reference sign are identical or equivalent toeach other. This notation applies through the entire specification. Inaddition, any configuration of the components described in the entirespecification is merely exemplary, and thus the present invention is notlimited by the description.

FIG. 1 is a schematic view illustrating the air-conditioning apparatus100 according to Embodiment 1 of the present invention. As illustratedin FIG. 1, the air-conditioning apparatus 100 includes a compressor 1, afour-way valve 2, an outdoor heat exchanger 3, an expansion valve 4, andan indoor heat exchanger 5. The compressor 1, the four-way valve 2, theoutdoor heat exchanger 3, the expansion valve 4, and the indoor heatexchanger 5 are, for example, sequentially connected by pipes to form arefrigerant circuit 90.

The compressor 1 is a variable capacity compressor configured tocompress sucked refrigerant and discharge the refrigerant ashigh-temperature and high-pressure refrigerant. The four-way valve 2 isa switching device that switches a direction in which the refrigerantdischarged from the compressor 1 flows, in response to, for example,execution of a heating operation or a cooling operation. The four-wayvalve 2 is provided closer to the discharge side of the compressor 1than the outdoor heat exchanger 3 and provided closer to the dischargeside of the compressor 1 than the indoor heat exchanger 5. FIG. 1illustrates an exemplary state in which the four-way valve 2 is switchedto perform a cooling operation. In FIG. 1, a solid line arrow indicatesthe flow of the refrigerant when the cooling operation is performed. InFIG. 1, a dashed line arrow indicates the flow of the refrigerant when aheating operation is performed.

The outdoor heat exchanger 3 is a heat exchanger configured to functionas a condenser at the cooling operation and function as an evaporator atthe heating operation. An outdoor side fan 31 is an air-sending unitconfigured to supply external air to the outdoor heat exchanger 3 andform airflow. The outdoor side fan 31 is, for example, an axial-flow fanor a centrifugal fan. The outdoor side fan 31 rotates when an outdoorside motor (not illustrated) is driven. Heat is exchanged between theair supplied from the outdoor side fan 31 and the refrigerant flowinginside the outdoor heat exchanger 3. The outdoor side fan 31 is drivenby a power unit (not illustrated) configured to supply electric power.

The expansion valve 4 is used to decompress and expand the refrigerantflowed out of the outdoor heat exchanger 3 at the cooling operation, anddecompress and expand the refrigerant flowed out of the indoor heatexchanger 5 at the heating operation.

The indoor heat exchanger 5 is a heat exchanger configured to functionas an evaporator at the cooling operation and function as a condenser atthe heating operation. An indoor side fan 51 is an air-sending unitconfigured to supply indoor air to the indoor heat exchanger 5 and formairflow. The indoor side fan 51 is, for example, an axial-flow fan or acentrifugal fan. The indoor side fan 51 rotates when an indoor sidemotor (not illustrated) is driven. Heat is exchanged between the airsupplied from the indoor side fan 51 and the refrigerant flowing insidethe indoor heat exchanger 5.

An outdoor side refrigerant temperature sensor 32 is a temperaturedetection unit configured to detect the temperature of the refrigerantflowing through the outdoor heat exchanger 3. An indoor side refrigeranttemperature sensor 52 is a sensor configured to detect the temperatureof the refrigerant flowing through the indoor heat exchanger 5. In thefollowing description, a “refrigerant temperature” refers to thetemperature of the refrigerant flowing inside the outdoor heat exchanger3.

A controller 80 controls the outdoor side motor to control the rotationspeed of the outdoor side fan 31, and controls the indoor side motor tocontrol the rotation speed of the indoor side fan 51. The controller 80controls the outdoor side motor by changing voltage and current input tothe outdoor side motor. The control of the rotation speed of the outdoorside fan 31 by the controller 80 allows control of the volume of airpassing through the outdoor heat exchanger 3.

A rotation speed detection unit configured to detect the rotation speedof the outdoor side fan 31 may be provided to detect the currentrotation speed of the outdoor side fan 31. Alternatively, the currentrotation speed of the outdoor side fan 31 may be estimated frominformation on current applied to the outdoor side motor and voltageapplied to the outdoor side motor. In the following description, a “faninput” refers to a physical value related to electric power supplied tothe outdoor side fan 31 (the outdoor side motor configured to rotate theoutdoor side fan 31).

The controller 80 controls the indoor side motor so that the outdoorside fan 31 rotates, for example, when the air-conditioning apparatus100 starts operating. The controller 80 is, for example, hardware suchas a circuit device or software executed on an arithmetic device such asa microcomputer or a CPU, which are configured to achieve thisfunctionality.

The cooling operation is executed when the controller 80 switches thefour-way valve 2 to cooling. The heating operation is executed when thecontroller 80 switches the four-way valve 2 to heating. In the followingdescription, a “defrosting operation” refers to an operation executedwhen the controller 80 switches the four-way valve 2 to cooling andstops the outdoor side fan 31. The heating operation corresponds to a“first operation” of the present invention, and the defrosting operationcorresponds to a “second operation” of the present invention.

The following first describes, with reference to FIG. 1, the flow of therefrigerant when the air-conditioning apparatus 100 of the presentinvention executes the cooling operation. The refrigerant dischargedfrom the compressor 1 flows into the outdoor heat exchanger 3. Havingflowed into the outdoor heat exchanger 3, the refrigerant exchanges heatwith the air supplied to the outdoor heat exchanger 3 through rotationof the outdoor side fan, and then flows out of the outdoor heatexchanger 3. Having flowed out of the outdoor heat exchanger 3, therefrigerant flows in the expansion valve 4 and is depressurized therein,and then flows out of the expansion valve 4 before flowing into theindoor heat exchanger 5. Having flowed into the indoor heat exchanger 5,the refrigerant exchanges heat with the air supplied to the indoor heatexchanger 5 through rotation of the indoor side fan, and then flows outof the indoor heat exchanger 5. Having flowed out of the indoor heatexchanger 5, the refrigerant flows into the compressor 1.

The following describes, with reference to FIG. 1, the flow of therefrigerant when the air-conditioning apparatus 100 of the presentinvention executes the heating operation. The refrigerant dischargedfrom the compressor 1 flows into the indoor heat exchanger 5. Havingflowed into the indoor heat exchanger 5, the refrigerant exchanges heatwith the air supplied to the indoor heat exchanger 5 through rotation ofthe indoor side fan, and then flows out of the indoor heat exchanger 5.Having flowed out of the indoor heat exchanger 5, the refrigerant flowsin the expansion valve 4 and is depressurized therein, and then flowsout of the expansion valve 4 before flowing into the outdoor heatexchanger 3. Having flowed into the outdoor heat exchanger 3, therefrigerant exchanges heat with the air supplied to the outdoor heatexchanger 3 through rotation of the outdoor side fan, and then flows outof the outdoor heat exchanger 3. Having flowed out of the outdoor heatexchanger 3, the refrigerant flows into the compressor 1.

FIG. 2 is a diagram illustrating change in a frosting amount and totalelectric power with elapsed time in the air-conditioning apparatus 100according to Embodiment 1 of the present invention. FIG. 3 is a diagramillustrating change in the frosting amount and total current value withelapsed time in the air-conditioning apparatus 100 according toEmbodiment 1 of the present invention.

In FIG. 2, the horizontal axis represents elapsed time [min], and thevertical axis represents the frosting amount [g] and a total electricpower amount [W]. In FIG. 2, a solid line indicates the frosting amount,and a dashed line indicates the total electric power. As illustrated inFIG. 2, the frosting amount increases as time elapses, and the totalelectric power increases as time elapses.

In FIG. 3, the horizontal axis represents elapsed time [min], and thevertical axis represents the frosting amount [g] and a total currentvalue [A]. In FIG. 3, a solid line indicates the frosting amount, and adashed line indicates the total current value. As illustrated in FIG. 3,the frosting amount increases as time elapses, and the total currentvalue increases as time elapses.

FIG. 4 is a diagram illustrating change in an electric power amount withelapsed time in the air-conditioning apparatus 100 according toEmbodiment 1 of the present invention. FIG. 5 is a diagram illustratingchange in the total electric power amount with elapsed time in theair-conditioning apparatus 100 according to Embodiment 1 of the presentinvention. FIGS. 4 and 5 illustrate a case in which the fan input is theelectric power amount, which is the product of current value applied toan outdoor fan motor and voltage value applied to the outdoor fan motor.Processing illustrated in FIGS. 4 and 5 is performed at the heatingoperation.

First, as illustrated in FIG. 4, the controller 80 detects the fan inputand calculates the amount of change in the fan input at each elapse of apredetermined time. Specifically, for example, when the fan input attime (t−1) is represented by W(t−1) and the fan input at time t isrepresented by W(t), the controller 80 calculates ΔW(t) as thedifference between the fan inputs through Expression (1.1) below.

ΔW(t)=W(t)−W(t−1)  (1.1)

Subsequently, as illustrated in FIG. 5, the controller 80 calculatesΔWtotal by summing ΔW(t) according to Expression (1.2) below.

ΔWtotal=ΣΔW(t)  (1.2)

Then, the controller 80 determines whether ΔWtotal is equal to or largerthan a threshold α as in Expression (1.3) below. When having determinedthat ΔWtotal is equal to or larger than the threshold α, the controller80 controls the four-way valve 2 to start the defrosting operation. Whenhaving determined that ΔWtotal is smaller than the threshold α, thecontroller 80 continues the heating operation.

ΔWtotal≧α  (1.3)

The threshold α varies with the refrigerant temperature. Specifically,for example, it is assumed that the density of frost on the outdoor heatexchanger 3 is larger at α higher refrigerant temperature, and thus thecontroller 80 decreases the value of a accordingly. When the value of αis decreased in this manner, ΔWtotal becomes equal to or larger than αat earlier timing and the defrosting operation is started earlier. Forexample, it is assumed that the density of frost on the outdoor heatexchanger 3 is smaller at a lower refrigerant temperature, and thus thecontroller 80 increases the value of α accordingly. When the value of αis increased in this manner, ΔWtotal becomes equal to or larger than αat later timing and start of the defrosting operation is delayed. In theabove description, the fan input is the electric power, but the presentinvention is not limited thereto. For example, the fan input may be thecurrent value applied to the outdoor fan motor or the voltage valueapplied to the outdoor fan motor.

FIG. 6 is a schematic view illustrating a state in which frost exists onthe outdoor heat exchanger 3 of the air-conditioning apparatus 100according to Embodiment 1 of the present invention. As illustrated inFIG. 6, the frost on the outdoor heat exchanger 3 has a height Hf_total[mm], and adjacent fins 3 b are apart from each other by a distance Fp[mm]. It is assumed that wind blows from one end of each fin 3 b in thelongitudinal direction thereof to the other end. Since frost exists onthe outdoor heat exchanger 3 as illustrated in FIG. 6, a wind speed uadecreases, and thus heat exchange at the outdoor heat exchanger 3 ishindered as compared to a case in which no frost exists on the outdoorheat exchanger 3.

In the heating operation, frost exists on a heat transfer tube 3 a andthe fins 3 b included in the outdoor heat exchanger 3. As the frostgrows, draft resistance increases and input of the outdoor side fan 31increases. The frost has a lower density as the heat transfer tube 3 aand the fins 3 b have lower temperatures. In other words, the frostdensity is smaller at a lower refrigerant temperature.

Thus, when the fins 3 b is blocked, the amount of frost on the outdoorheat exchanger 3 differs for different frost densities. In other words,the defrosting operation needs different defrosting heat amounts for anidentical blockage state of the outdoor heat exchanger 3 and anidentical amount of increase in the fan input. Specifically, at a higherrefrigerant temperature, a larger amount of heat is needed to melt froston the outdoor heat exchanger 3.

FIG. 7 is a diagram illustrating a relation between a relative humidityφ and a frost density ρ in the air-conditioning apparatus 100 accordingto Embodiment 1 of the present invention. In FIG. 7, the horizontal axisrepresents the relative humidity φ [%], and the vertical axis representsthe frost density ρ [kg/m³]. FIG. 7 illustrates cases with therefrigerant temperature Ts [degrees C.] at −30 degrees C. and −20degrees C.

As illustrated in FIG. 7, the frost density ρ decreases as the relativehumidity φ increases. The frost density ρ is larger when the refrigeranttemperature Ts is −20 degrees C. than when the refrigerant temperatureTs is −30 degrees C. In other words, the frost density ρ increases asthe refrigerant temperature Ts increases. A defrosting durationincreases as the frost density ρ increases, and a larger defrostingcapacity is needed as the frost density ρ increases. Thus, thedefrosting duration increases as the refrigerant temperature Tsincreases.

FIG. 8 is a diagram illustrating a relation between the refrigeranttemperature and a necessary defrosting heat amount in theair-conditioning apparatus 100 according to Embodiment 1 of the presentinvention. As illustrated in FIG. 8, the necessary defrosting heatamount is proportional to the temperature of the refrigerant flowingthrough the refrigerant circuit 90 inside the outdoor heat exchanger 3.

As illustrated in FIG. 8, the defrosting duration increases as therefrigerant temperature Ts increases. Specifically, for example, aminimum defrosting duration is one minute when an average refrigeranttemperature is −40 degrees C. to −30 degrees C. For example, the minimumdefrosting duration is three minutes when the average refrigeranttemperature is −10 degrees C. to −5 degrees C. For example, the minimumdefrosting duration is five minutes when the average refrigeranttemperature is −5 degrees C. to 0 degrees C.

Although FIG. 8 illustrates, for sake of simplicity of description, theproportional relation between the necessary defrosting heat amount andthe refrigerant temperature Ts, the present invention is not limited tosuch a relation. The amount of increase in the necessary defrosting heatamount for increase in the refrigerant temperature Ts does not need tobe constant.

FIG. 9 is a diagram illustrating change in the frequency of thecompressor 1 with elapsed time in the air-conditioning apparatus 100according to Embodiment 1 of the present invention. FIG. 10 is a diagramillustrating change in the frequency of the compressor 1 with elapsedtime in the air-conditioning apparatus 100 according to Embodiment 1 ofthe present invention.

In FIGS. 9 and 10, the horizontal axis represents elapsed time, and thevertical axis represents the frequency of the compressor 1. In FIGS. 9and 10, a solid line indicates change in the frequency of the compressor1 when the refrigerant temperature is relatively high, and a dashed lineindicates change in the frequency of the compressor 1 when therefrigerant temperature is relatively low.

The defrosting operation can be performed in a shorter time at arelatively low refrigerant temperature than at a relatively highrefrigerant temperature. However, efficient execution of the defrostingoperation requires a time for melting frost on the outdoor heatexchanger 3 and a time for allowing melted frost to drop from theoutdoor heat exchanger 3. Thus, melted frost potentially freezes againwhen the duration of the defrosting operation at a relatively lowrefrigerant temperature is shorter than the duration of the defrostingoperation at a relatively high refrigerant temperature. For this reason,in Embodiment 1, the operation is performed with identical defrostingdurations at a relatively low refrigerant temperature and a relativelyhigh refrigerant temperature and with a low frequency of the compressor1, which will be described below.

The following describes, with reference to FIG. 9, an example in whichthe frequency of the compressor 1 is changed based on the refrigeranttemperature in the defrosting operation. In FIG. 9, Interval (a) refersto an interval in which the heating operation is executed, Interval (b)refers to an interval in which the defrosting operation is executed, andInterval (c) refers to an interval in which the heating operation isexecuted after the defrosting operation.

As illustrated in FIG. 9, in Interval (a), the controller 80 controlsthe compressor 1 so that the compressor 1 has a predetermined frequencywhile the four-way valve 2 is switched to heating. After the compressor1 is operated at the predetermined frequency for a predetermined time,the controller 80 controls the compressor 1 to decrease the frequencythereof. Then, when the frequency of the compressor 1 becomes zero(t11), the controller 80 switches the four-way valve 2 to cooling andstarts the defrosting operation.

As illustrated in FIG. 9, in Interval (b), when the refrigeranttemperature is relatively high, the controller 80 controls thecompressor 1 so that the compressor 1 has a predetermined frequency fmaxwhile the four-way valve 2 is switched to cooling. After the compressor1 is operated at the predetermined frequency fmax for a predeterminedtime, the controller 80 controls the compressor 1 to decrease thefrequency of the compressor 1. Then, when the frequency of thecompressor 1 becomes zero (time t14), the controller 80 switches thefour-way valve 2 to heating again and starts the heating operation.

As illustrated in FIG. 9, in Interval (b), when the refrigeranttemperature is relatively low, the controller 80 controls the compressor1 so that the compressor 1 has the predetermined frequency fmax whilethe four-way valve 2 is switched to cooling. After the compressor 1 isoperated at the predetermined frequency fmax for a predetermined time(time t12), the controller 80 controls the compressor 1 to decrease thefrequency thereof so that the compressor 1 has a predetermined frequencyf1. After the frequency of the compressor 1 is decreased to thepredetermined frequency f1 (time t13), the controller 80 operates thecompressor 1 at the predetermined frequency f1 for a predetermined time.After the compressor 1 is operated at the predetermined frequency f1 forthe predetermined time (time t13), the controller 80 controls thecompressor 1 to decrease the frequency of the compressor 1. Then, whenthe frequency of the compressor 1 becomes zero (time t14), thecontroller 80 switches the four-way valve 2 to heating again and startsthe heating operation.

As illustrated in FIG. 9, in Interval (c), the controller 80 controlsthe compressor 1 so that the frequency thereof has a predeterminedfrequency while the four-way valve 2 is switched to heating.

The following describes, with reference to FIG. 10, an example in whichthe frequency of the compressor 1 is changed based on the refrigeranttemperature in the defrosting operation. In FIG. 10, Interval (a) refersto an interval in which the heating operation is executed, Interval (b)refers to an interval in which the defrosting operation is executed, andInterval (c) refers to an interval in which the heating operation isexecuted after the defrosting operation. In FIG. 10, change in thefrequency of the compressor 1 as time elapses in Interval (a) andInterval (c) is identical to that in FIG. 9, and thus descriptionthereof will be omitted.

As illustrated in FIG. 10, in Interval (b), when the refrigeranttemperature is relatively high, the controller 80 controls thecompressor 1 so that the compressor 1 has the predetermined frequencyfmax while the four-way valve 2 is switched to cooling. After thecompressor 1 is operated at the predetermined frequency fmax for apredetermined time, the controller 80 controls the compressor 1 todecrease the frequency of the compressor 1. Then, when the frequency ofthe compressor 1 becomes zero (time t24), the controller 80 switches thefour-way valve 2 to heating again and starts the heating operation.

As illustrated in FIG. 10, in Interval (b), when the refrigeranttemperature is relatively low, the controller 80 controls the compressor1 so that the compressor 1 has a predetermined frequency f2 while thefour-way valve 2 is switched to cooling. After the compressor 1 acquiresthe predetermined frequency f2 (time t22) and has operated for apredetermined time (time t23), the controller 80 controls the compressor1 to decrease the frequency of the compressor 1. Then, when thefrequency of the compressor 1 becomes zero (time t24), the controller 80switches the four-way valve 2 to heating again and starts the heatingoperation.

As described above, in the air-conditioning apparatus 100 according toEmbodiment 1, the compressor 1, the outdoor heat exchanger 3, the indoorheat exchanger 5, and the four-way valve 2 provided closer to thedischarge side of the compressor 1 than the outdoor heat exchanger 3 andprovided closer to the discharge side of the compressor 1 than theindoor heat exchanger 5 are connected with each other. Theair-conditioning apparatus 100 includes the fan 31 configured to deliverair toward the outdoor heat exchanger 3, the power unit configured tosupply electric power to the fan 31, a fan input detector configured todetect a physical value related to the electric power supplied to thefan 31, and the controller 80 configured to control the four-way valve 2to switch between the first operation in which the outdoor heatexchanger 3 functions as an evaporator and the second operation in whichthe outdoor heat exchanger 3 functions as a condenser. The firstoperation is switched to the second operation when the physical valuedetected by the fan input detector is equal to or larger than areference value. The controller 80 adjusts the reference value so thatthe reference value when the refrigerant flowing through the outdoorheat exchanger 3 has a high temperature is smaller than the referencevalue when the refrigerant has a low temperature. With thisconfiguration, the defrosting operation can be started at appropriatetiming when the heating operation is performed. Accordingly, thedefrosting operation can be performed more efficiently thanconventionally practiced.

In the air-conditioning apparatus 100 according to Embodiment 1, thecompressor 1, the outdoor heat exchanger 3, the indoor heat exchanger 5,and the four-way valve 2 provided closer to the discharge side of thecompressor 1 than the outdoor heat exchanger 3 and provided closer tothe discharge side of the compressor 1 than the indoor heat exchanger 5are connected with each other. The air-conditioning apparatus 100includes the fan 31 configured to deliver air toward the outdoor heatexchanger 3, the power unit configured to supply electric power to thefan 31, the fan input detector configured to detect a physical valuerelated to the electric power supplied to the fan 31, and the controller80 configured to control the four-way valve 2 to switch between thefirst operation in which the outdoor heat exchanger 3 functions as anevaporator and the second operation in which the outdoor heat exchanger3 functions as a condenser. The first operation is switched to thesecond operation when the physical value detected by the fan inputdetector is equal to or larger than a reference value. The controller 80controls the frequency of the compressor 1 so that the frequency of thecompressor 1 when the refrigerant flowing through the outdoor heatexchanger 3 has a high temperature is higher than the frequency of thecompressor 1 when the refrigerant has a low temperature. With thisconfiguration, the defrosting operation can be performed in accordancewith the frosting amount more appropriately than conventionallypracticed. Accordingly, the defrosting operation can be performed moreefficiently than conventionally practiced.

Embodiment 2

In Embodiment 2, unlike Embodiment 1, the timing of execution of thedefrosting operation is determined based on a frosting amount Mf, andthe frequency of the compressor 1 in the defrosting operation isdetermined based on the frosting amount Mf. In Embodiment 2, anycharacteristic is same as that of Embodiment 1 unless otherwise stated,and any identical function and configuration will be described by usingidentical reference signs.

The frosting amount mf(t) is given based on a surface area A0 [m²], thefrost density ρf [kg/m³], and a frost height Hf(t) through Expression(2.1) below.

mf(t)=A0×ρf(t)×Hf(t)  (2.1)

Expression (2.1) below assumes that frost uniformly exists on theoutdoor heat exchanger 3. The surface area A0 [m²] is a heat exchangesurface area of the outdoor heat exchanger 3. The frost density ρf[kg/m³] is the density of frost on the outdoor heat exchanger 3, whichis affected by a cooling surface temperature and a relative humidity.The frost height Hf(t) is the height of frost on the outdoor heatexchanger 3.

The frosting amount Mf is given based on the frosting amount mf(t)through Expression (2.2) below.

Mf=Σm(t)  (2.2)

A defrosting heat amount Qf [kJ] is given based on the frosting amountMf [kg] and a latent heat ΔH [kJ/kg] through Expression (2.3) below.

Qf=Mf×ΔH  (2.3)

A defrosting duration Tf [sec] is given based on the defrosting heatamount Qf [kJ] and a defrosting capacity P [kW] through Expression (2.4)below.

Tf=Qf/P  (2.4)

As described above, the controller 80 of the air-conditioning apparatus100 according to Embodiment 2 determines the defrosting duration inaccordance with the frosting amount. Accordingly, the defrostingoperation can be performed more efficiently than conventionallypracticed.

The outdoor side fan 31 corresponds to a “fan” of the present invention.

REFERENCE SIGNS LIST

1 compressor 2 four-way valve 3 outdoor heat exchanger 3 a heat transfertube 3 b fin 4 expansion valve 5 indoor heat exchanger 31 outdoor sidefan 32 outdoor side refrigerant temperature sensor 51 indoor side fan 52indoor side refrigerant temperature sensor 80 controller 90 refrigerantcircuit 100 air-conditioning apparatus A0 surface area f1, f2, fmaxpredetermined frequency Hf frost height Mf frosting amount mf frostingamount P defrosting capacity Qf defrosting heat amount t11, t12, t13,t14, t21, t22, t23, t24 time Tf the defrosting duration Ts surfacetemperature ua wind speed ΔH latent heat α threshold ρ frost density ρffrost density φ relative humidity

1. An air-conditioning apparatus comprising: a compressor, an outdoorheat exchanger; an indoor heat exchanger; a switching device, theswitching device being provided closer to a discharge side of thecompressor than the outdoor heat exchanger and provided closer to thedischarge side of the compressor than the indoor heat exchanger, thecompressor, the outdoor heat exchanger, the indoor heat exchanger, andthe switching device being connected one another; a fan configured todeliver air toward the outdoor heat exchanger; a power unit configuredto supply electric power to the fan; a fan input detector configured todetect a physical value correlated to the electric power supplied to thefan; and a controller configured to control the switching device toswitch between a first operation in which the outdoor heat exchangerserves as an evaporator and a second operation in which the outdoor heatexchanger serves as a condenser, wherein the first operation is switchedto the second operation when the physical value detected by the faninput detector is equal to or larger than a reference value, and whereinthe controller is configured to adjust the reference value such that thereference value when a refrigerant temperature flowing in the outdoorheat exchanger is high to be lower than the reference value when therefrigerant temperature flowing in the outdoor heat exchanger is low. 2.An air-conditioning apparatus comprising: a compressor; an outdoor heatexchanger; an indoor heat exchanger; a switching device, the switchingdevice being provided closer to a discharge side of the compressor thanthe outdoor heat exchanger and provided closer to the discharge side ofthe compressor than the indoor heat exchanger, the compressor, theoutdoor heat exchanger, the indoor heat exchanger, and the switchingdevice being connected one another; a fan configured to deliver airtoward the outdoor heat exchanger; a power unit configured to supplyelectric power to the fan; a fan input detector configured to detect aphysical value correlated to the electric power supplied to the fan; anda controller configured to control the switching device to switchbetween a first operation in which the outdoor heat exchanger serves asan evaporator and a second operation in which the outdoor heat exchangerserves as a condenser, wherein the first operation is switched to thesecond operation when the physical value detected by the fan inputdetector is equal to or larger than a reference value, and wherein thecontroller is configured to control the compressor such that frequencyof the compressor when a refrigerant temperature flowing in the outdoorheat exchanger is high to be higher than the frequency of the compressorwhen the refrigerant temperature flowing in the outdoor heat exchangeris low.
 3. The air-conditioning apparatus of claim 1, wherein the faninput detector detects a current value or a voltage value applied to anoutdoor side motor configured to drive the fan, or electric power basedon the current value and the voltage value.
 4. The air-conditioningapparatus of claim 2, wherein fan input detector detects a current valueor a voltage value applied to an outdoor side motor configured to drivethe fan, or electric power based on the current value and the voltagevalue.